1. Field of the Invention:
The present invention relates generally to the fabrication of well pipes which are utilized in the production of hydrocarbon fluids, and in particular, to a method and apparatus for fabricating threads on the connecting ends of such pipes.
2. Description of the Prior Art:
The production of hydrocarbon fluids such as oil and gas from deep earth strata present serious problems not encountered in shallower hydrocarbon producing wells. Well pipes, usually fabricated of ferrous metals, are commonly employed in connection with the drilling of such wells into the earth and in the production of fluids from the wells. Generally, the well pipes have lengths convenient for handling and carry threaded joints at their ends so that the lengths of the well pipe can be readily interconnected. The joints of well pipe may typically be from 20 to 35 feet in length and may be connected together to form pipe strings to reach the producing strata, which may be located at depths of from 10,000 to 20,000 feet.
The well pipe in very deep wells may be subjected to great fluid pressures and highly corrosive fluids. Thus, the joints between the well pipe sections in a pipe string must be able to contain such internal pressures and also the tensile stresses induced by the weight of the pipe string. The connections must be strong in tension, torsion, pressure resistance, and in handling strength so that the well pipe will perform under many special conditions. For example, drill tubing connections must be strong enough to be made up and broken repeatedly without failure. This requires that the burst and collapse strength of the threaded connection should be equal to or greater than the burst and collapse strength of the pipe body. Increased burst and collapse strength for the threaded connection has been provided by forming a mechanical "upset" on the end of the well pipe or tubing. The mechanical upset is formed during the fabrication of the pipe section by heating the pipe to a high temperature and compressing the pipe in a die by a compressive force which exceeds the yield strength of the pipe metal. This procedure provides an enlarged wall thickness on the end of the pipe in which connecting threads are machined. Another method of enlarging the wall thickness of a pipe to form threaded connections and the like is disclosed in U.S. Pat. No. 1,577,591, wherein tapered metal sleeves are welded to the inner and outer surfaces of a pipe and male and female tool joint members are formed therein.
The mechanically upset well pipe connection has been used successfully and has found wide acceptance in the industry, especially for well pipes constructed of conventional ferrous alloys. However, corrosion resistant alloy materials such as stainless steel have been used to fabricate the joints which are utilized in the lower portions of deep wells which produce highly corrosive fluids. Because of the difficulties and expense involved in forming a mechanical upset in those alloys, the use of a solid stainless steel system has been limited to a relatively small number of wells of high production capacity.